For example, Patent Document 1 discloses a solenoid in which a mold coil (coil case) and a solenoid main body (case member) are integrated by a snap ring (retaining ring) mounted between a groove formed in an outer peripheral surface of the mold coil and a groove formed in an inner peripheral surface of the case. By the way, in a case in which the solenoid is applied to an actuator configured to regulate a damping force of a damping force regulation type damper in a semi-active suspension mounted in a vehicle, there is a problem in that abnormal noise is generated from the solenoid due to a play in a direction along an axis of the solenoid (hereinafter, referred to as an “axial direction”) due to an axial gap between the retaining ring and the groove, or a degree of design flexibility of a magnetic circuit is restricted.
In order to eliminate the play, it has been proposed to sandwich an O-ring at an outer peripheral-side position of the retaining ring in the axis direction by the mold coil and the solenoid main body. However, because the solenoid increases in diameter in a radial direction (which requires the increase in thickness), the size of the solenoid is increased.